Ultra high efficiency/low pressure supercritical fluid chromatography (UHE/LP-SFC) for triglyceride analysis: Identification, quantification, and classification of vegetable oils

Abstract

Triglycerides of vegetable oils have been extensively studied. Non-aqueous reversed-phase liquid chromatography and silver-ion chromatography are most frequently used to achieve their separation. In previous works, we presented the use of supercritical fluid chromatography with long columns (75 cm) packed with fused-core particles to provide ultra-high-performance separations, with a low-toxicity fluid (carbon dioxide) compared to the usual liquid-phase methods. In the present paper, we describe the quantification of triglycerides with supercritical fluid chromatography and evaporative light-scattering detection. Thanks to the isocratic elution mode, this quantification can be simplified, assuming (a) identical response coefficients for compounds having a close structure, (as only triglycerides are quantified), and (b) constancy of the response coefficient along the analysis (no elution gradient). Therefore, the relative concentrations of triglycerides were easily assessed. Only one calibration curve for one reference compound (in this case triolein) was required. The resulting relative concentrations are in good accordance with the numerous publications available. Relative quantification with UV detection at 210 nm is also proposed, facilitated by the very low UV absorption of carbon dioxide and with a calibration curve taking account of the variation of UV response according to double bond number. Nineteen vegetable oils are compared. The identification of triglycerides was carried out based on previous knowledge of these oils, but also with the help of a Goiffon retention diagram, based on the relationship between the logarithm of retention factor and the total double bond number. Finally, cluster analyses were computed, based on evaporative light-scattering detection or UV quantification data. They allow a quick comparison of the triglyceride content between the oils, in the goal to exchange one by the other for certain applications, or to compare a new oil to well-known ones.